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Old 4th September 2004, 10:18 AM   #1
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Default WTB: big toobs

I need as many big tubes as possible. Example: up to seven 3-500Zs for a total plate dissipation of 3.5kW. One 4CX3500A would do it. Anything in the 100W range is just about useless as well, I'd need 35...LOL. This is for an induction heater project with maximum input of 10kW from the supply.

Tim
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Old 4th September 2004, 05:32 PM   #2
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You mention triodes in one breath and a large tetrode in another. I would suggest that if your induction heater oscillator is self driven you do NOT want to fool with anything but big bad boy triodes for this project.

I could have the machine you are trying to build already built for sale. It operates at 100 KHz and has three 5 kW forced air cooled BR1160 EEV triodes in it. It can produce much more power with an outboard plate xfmer but with the internal one processes 6.5 kW in for 5 kW RF out. It runs on 220 volt single phase domestic power. I built it to simulate a CW broadcast transmitter to test insulators for breakdown.

PM me if interested. It is priced to be very good value for a company buying a piece of laboratory equipment, not for the casually curious hobbyist. It is near Toronto and I will not ship this. Bring or send a truck for it only.
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Old 4th September 2004, 07:08 PM   #3
316a is offline 316a  England
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Default Re: WTB: big toobs

Quote:
Originally posted by Sch3mat1c
I need as many big tubes as possible. Example: up to seven 3-500Zs for a total plate dissipation of 3.5kW. One 4CX3500A would do it. Anything in the 100W range is just about useless as well, I'd need 35...LOL. This is for an induction heater project with maximum input of 10kW from the supply.

Tim
Hello ,
I think I have a few 3/500Z somewhere , these look like a squarish goldfish bowl from memory . Otherwise look for 715B . Completely useless and usually cheap on Ebay . GK71 are also cheap and can chuck out 250W of class C which I guess you'll be using

cheers

316a
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Old 5th September 2004, 01:52 AM   #4
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Quote:
Originally posted by rcavictim
You mention triodes in one breath and a large tetrode in another. I would suggest that if your induction heater oscillator is self driven you do NOT want to fool with anything but big bad boy triodes for this project.
I'm torn on this point. For one, pentodes will allow screen-voltage throttling quite easily. i'm not sure how best to control triodes, grid voltage coupling I guess. Yes, it will be self-excited. Probably 20 to 100kHz depending on how much capacitance I put on the coil.

Quote:

PM me if interested. It is priced to be very good value for a company buying a piece of laboratory equipment, not for the casually curious hobbyist. It is near Toronto and I will not ship this. Bring or send a truck for it only.
Interesting, but I intend to build this myself (I already have the transformer after all, and there's not much else I can use 800VAC for!), and I'm a bit far from Toronto anyway.

Tim
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Old 5th September 2004, 02:00 AM   #5
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I've always used B+ voltage throttling on my triode based self excited RF power oscillators. 800 volts isn't enough to get much out of any of the tubes best suited for industrial heating. The machine I described runs 4500 VDC at an amp and a half.

If you cannot find a suitable large plate xfmer you can use a utility pole pig. They can be had for just a couple to three hundred bucks in 10 kVA class.
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Old 5th September 2004, 03:23 AM   #6
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I worked as a field service technician for a Milwaukee induction heating equipment firm and every one I saw used a 3 phase motor controller to turn the plate transformer on and off as well as power control by turning the AC off at some time during the sine wave. All were a single big tube run at thousands of volts. The machines running at the lower voltages you mentioned were solid state using big hockey puck SCR's. Most of the tube ones were self excited oscillators at around 400 Khz. The biggest problem is in cooling of the tube. Any questions feel free to e-mail.
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Old 5th September 2004, 07:46 AM   #7
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Yeah, I'll be using a doubler at least and probably a quadrupler. No good using solid state unfortunately, as the voltage is too high no matter what.

Tim
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Old 5th September 2004, 04:56 PM   #8
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You're gonna pull 10 kW out of a quadrupler? Plan on mortgaging your home to buy capacitors that can handle that abuse. Save yourself a lot of grief and buy a pole pig. BTW, I use SS rectification on my system. You can also use Hg Thyratrons (as half the rectifier elements) and get the phase angle power control spoken of by dshortt9.

I've got the big thyratrons, and their filament and control transformers that I pulled from a pair of 10 kW RCA BTA10K AM broadcast transmitters when gathering parts for my project. I don't need them.
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Old 6th September 2004, 12:48 AM   #9
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Meh, about 2A average at 4kV, I'll have to check on resistances and power factor but a few computer grade caps in series and parallel will handle it. Might derate to 5kW, especially since the transformer has magnetic shunts in it. In which case, I still need about 1-2kW of plate dissipation.

Tim
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Old 7th September 2004, 03:11 AM   #10
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rcavictim, what are the thyratrons you have? I'm looking to replace my JAN 5948.
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